[Scilab-users] Xcos PID controller problem

[Serge Steer]

The PID controller is an improper transfer function (degree of 
num>degree of den). In Xcos the derivative term of the PID bloc is 
computed by an approximation
which seems to fail in your context.

A solution should be to replace the PID bloc with a transfert function 
block made proper adding a very small term in s^2 for the denominator 
(sse the attched diagram)

Please report the problem in http://bugzilla.scilab.org/

Serge Steer

Le 17/02/2014 21:51, john a écrit :
> Hello,
> I'm new to Scilab and Xcos so may be making a simple mistake, but I have the
> following problem.  I created an Xcos model of a simple mass-spring-damper
> with PID control using the data from the Matlab example shown  here
> <http://ctms.engin.umich.edu/CTMS/index.php?example=Introduction&section=ControlPID>
> .
>
> The Xcos results are the same as the Matlab example except for the case when
> all three gains are used as follows Kp=350, Ki=300 and Kd=50 .
>
> My result looks like this (red line) and is clearly giving a different
> response to the Matlab example for the same gain values.
>    <http://mailinglists.scilab.org/file/n4028669/PID.png>
> I have tried different solvers and time steps, but this doesn't seem to be
> the problem.  I have also modelled the problem in Mathcad 7, Mathcad Prime 3
> and using csim in Scilab and all those results agree broadly with the Matlab
> example.
>
> Any advice would be greatly appreciated and I have attached the Xcos file
> for information. spring-damper-PID.zcos
> <http://mailinglists.scilab.org/file/n4028669/spring-damper-PID.zcos>
>
>
>
>
> --
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